Tractor-trailer coupling detection

ABSTRACT

To test whether a trailer is coupled to a tractor when the tractor ignition switch is off, a test switch in the trailer connects a high-impedance power source in a trailer to a line carrying energy from the tractor ignition switch to the trailer&#39;s electrical load, and measures the voltage at the line. A high voltage indicates a connection only to the electrical load in the trailer and thus a decouple. A low voltage indicates a measurement of the electrical loads in both trailer and tractor and hence a coupling.

RELATED APPLICATIONS

This application claims the benefit of U.S. Application Ser. No.60/896,491 filed 22 Mar. 2007, U.S. Application Ser. No. 60/908,467filed 28 Mar. 2007, and U.S. Application Ser. No. 60/908,588 filed 28Mar. 2007. This application is a continuation of U.S. application Ser.No. 12/054,380 filed 24 Mar. 2008, now U.S. Pat. No. 7,911,330 issued 22Mar. 2011. The contents of these applications are hereby incorporatedherein as if fully recited herein.

FIELD OF THE INVENTION

This invention relates to trailer-mounted telematics system, andparticularly to telematics system for accurately detecting when atrailer is or is not coupled to a tractor.

BACKGROUND OF THE INVENTION

In present systems, when a tractor connects to a trailer, the operatorcompletes an electrical connection through a cable between the two unitsto provide electrical power to the trailer for operation of the lightsand the anti-lock braking system. Various devices serve to indicate whenthe connection is broken. However, when the tractor's ignition isswitched off while still connected to a trailer, such as during a stopen route for the driver to sleep or eat the trailer has no way ofdetermining whether the tractor has in fact been decoupled or if thetractor has merely been shut off.

An object of this invention is to overcome this and other problems inthe system.

SUMMARY OF EMBODIMENTS OF THE INVENTION

According to an embodiment of the invention, when the tractor ignitionswitch is off, a test switch in the trailer connects a high-impedancepower source in a trailer to a line carrying energy from the tractorignition switch to the trailer's electrical load, and a meter measuresthe voltage at the line, so that one voltage denotes only the electricalload in the trailer and thus a decouple, and another voltage denotes theelectrical loads in both trailer and tractor and hence a coupling.

The various features of novelty characterizing the invention are pointedout in the claims. Other objects and advantages of the invention willbecome evident from the following detailed description when read inlight of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating an embodiment of theinvention.

FIG. 2 is a schematic diagram illustrating another embodiment of theinvention incorporating the embodiment of FIG. 1.

FIG. 3 is a flow chart illustrating the operation embodying an aspect ofthe invention.

FIG. 4 is a flow chart illustrating the operation embodying anotheraspect of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the embodiment of FIG. 1, a tractor TC1 and a trailer TL1 areelectrically connected by means of a multi-pin “J560” connector 5through an auxiliary/ABS (antilock brake system) line 9 and a groundline 10. Other circuits within this multi-pin connector 5 carry othersignals, for example to control trailer lights. When an ignition switch6 within the tractor TC1 is closed, battery voltage from a battery 7appears at ignition switch loads 8 and other electrical loads within thetractor TC1. The closed ignition switch 6 and a pin within the multi-pinconnector 5 also place the voltage at the battery 7 onto the trailer'selectrical loads 12 (primarily an antilock brake module). Avoltage-measuring device 3 in the trailer TL1 senses the voltage presentat the line 9 relative to ground 10.

When the tractor TC1 is running and is connected to the trailer TL1,ignition switch 6 is closed and voltage on the battery 7 appears at thesignal line 9. Circuitry in 3 detects the voltage on battery 7 andinforms a controller 11 mounted within the trailer TL1 that it has beenconnected to the tractor TC1. Should the tractor TC1 become disconnectedfrom the trailer TL1, the voltage on 9 will vanish, and the trailersensing system will correctly infer that it is no longer connected to atractor.

At installation time, the trailer system is calibrated to the electricalloads present. The trailer TL1 is left unconnected to any tractor, and aswitch 4 is closed. This allows current to pass through resistor 2 tothe trailer loads 12 on the Auxiliary/ABS line 9. The voltage on theline is read by means of meter 3, which may alternatively be ananalog-to-digital converter. Controller 11 stores the value obtained.Resistor 2 is selected to give a small voltage drop during thiscalibration phase.

When the tractor's ignition switch 6 is opened while the tractor TC1 isstill connected to the trailer TL1, voltage is no longer present at line9. The controller 11 detects the absence of the voltage at line 9 bysensing the voltage from the meter 3, and now determines if this loss ofvoltage is due to a disconnect between tractor TC1 and trailer TL1, orto the ignition switch 6 in the tractor TC1 being switched off. To dothis, the controller 11 responds to the absence of signal at meter 3 andcloses the switch 4, thereby causing a test current to flow throughresistor 2 to the line 9 and to the meter 3. The meter 3 again measuresthe voltage on the line 9. Should this voltage be a value stored duringthe calibration phase, the controller 11 correctly infers that there hasbeen a true disconnect of the trailer TL1 from the tractor TC1.

Should the tractor TC1 still be connected to the trailer TL1, then theother electrical loads 8 within the tractor TC1 will draw current at alevel higher than was measured during calibration. The voltage measuredat meter 3 will fall to a value below the calibration value. Thecontroller 11 will correctly interpret this as an ignition switchturn-off rather than a tractor disconnect. The controller 11 operates atransmitter TR1 that transmits the information concerning connect ordisconnect. According to one embodiment of the invention, thetransmitter TR1 is part of the controller 11. According to anotherembodiment the transmitter TR1 is external to the controller. Accordingto another embodiment the transmitter TR1, while external to thecontroller 11, still remains part of the controller

FIG. 2 illustrates a trailer fleet of a number of tractor/trailercombinations, wherein each tractor is designated TC1 and each trailerTR1, and wherein each tractor and each trailer includes the respectivecircuitry shown in FIG. 1. In FIG. 1, the controller 11 includes thetransmitter, shown in FIG. 2 as TR1, that transmits the connect ordisconnect information from each tractor/trailer combination to awireless link WL1 that transfers the data to a Network Operations CenterNOC. An internet link conveys the data to Fleet Managers FM1 that usethe facts to help manage the fleet.

FIG. 3 is a flow chart illustrating the operation of the controller 11during calibration. Here, the calibration starts with step 110 byunhooking the trailer TL1 from the tractor TC1. Step 120 follows byclosing switch 4 and reading the voltage with meter 3 in step 130. Instep 140 a memory in the controller 11 stores the voltage of meter 3,and in step 150 the switch 4 is opened to end the calibration as shownat 160.

FIG. 4 is a flow chart illustrating the operation of the controller 11during normal operation. At the outset the controller 11 stores thehooked or unhooked (i.e. coupled or uncoupled) state that was previouslydetermined. In the absence of an initial current coupling state storedin the controller 11, the latter signals a default state of “unhooked”,i.e. uncoupled. In step 210 a clock in the controller 11 initiates atest signal periodically, such as every minute to actuate adetermination of the current (i.e. existing) state. The controller thencompares the current state with the stored state as it pre-existed justprior to each periodic signal. As indicated, the stored coupling statemay be the default state of “unhooked” or uncoupled.

If controller 11 has stored an indication that the trailer waspreviously hooked, step 230 checks the voltage at meter 3. If thevoltage at step 230 is approximately 12 volts this indicates in step 240that the trailer TL1 is still hooked. The controller 11 then stores thehooked condition or state and transmits a signal to continue withperiodic testing at step 210. If the voltage at meter 3 in step 230 isapproximately 0 volts, the controller 11 executes step 250 and closesswitch 4. The controller 11, at step 260, checks the voltage at meter 3.At step 270 if the voltage is equal to the calibration voltage, thecontroller has detected an unhook indicating that the state is unhookedat step 280. At step 290 the transmitter in the controller 11 sends anunhooked message to the fleet managers via the wireless link WL1 and thecenter NOC. In step 300 the controller 11 opens the switch 4 and signalsto continue with step 210. The controller 11 stores this unhookcondition.

In step 260 if the voltage at meter 3 is less than the calibrationvoltage, step 310 indicates that the ignition switch 6 is off but thetrailer is hooked. The controller 11 opens the switch 4 in step 320 andreturns to step 210. The controller 11 stores the hooked state.

In step 210 a clock in the controller 11 continues to actuate adetermination of the current state in step 220. If the controller showsa state wherein the trailer is unhooked, step 330 checks the voltage atmeter 3. If the voltage is approximately 0 volts this indicates in step340 that the trailer TL1 is still unhooked. The controller 11 thentransmits a signal to continue with testing at step 210. The controllerstores this new unhooked state. If the voltage at meter 3 in step 330 isapproximately 12 volts, the controller at step 350 recognizes that thestatus in hooked. At step 360 the transmitter in the controller 11 sendsa hooked message to the fleet managers via the wireless link WL1 and thecenter NOC and signals the controller to continue at step 210. Thecontroller 11 the stores the newly hooked state.

The controller 11 thus sends a state message only when the current statechanges despite the periodic state tests. This limits the bandwidth andtransmission time used by the system in reporting changes.

The controller 11 is biased into the unhooked condition becausetypically the controller starts its operation as the trailer TL1 iscoupled to the tractor TC1. Thus, the coupling of trailer TL1 to tractorTC1 results in a change at step 330 to approximately 12 volts thatinitiates step 350 and causes the controller 11 to signal that thetrailer has become coupled to the tractor.

The embodiments of the invention allow a trailer-mounted telematicssystem to accurately detect when it is or is not coupled to a tractor.Upon change of coupling state, the system can wirelessly send a messageto its fleet manager, who can take appropriate action. When a tractorconnects to a trailer, the operator completes the electrical connectionbetween the two units by means of a 7-signal cable specified by SAEJ560. This allows the tractor to provide electrical power to the trailerfor operation of the lights and the anti-lock braking system. One way atrailer-mounted device can detect that it is coupled to a tractor is tomonitor the electrical status of the Auxiliary and ABS line (pin 7).This line is typically connected to the load side of the tractor'signition switch, and therefore is at ˜12 v when the tractor is running.If the trailer-mounted device senses voltage at this pin, it serves asan indication that it has been connected to a tractor; absence ofvoltage implies that the connection has been broken.

The embodiments of the invention overcome an anomaly that may exist whenthe tractor's ignition is switched off while still connected to atrailer. This may occur due to any number of reasons, among themstopping en route for the driver to sleep or eat. The embodiments of theinvention overcome the difficulty of merely monitoring the voltage ofthe Auxiliary and ABS signal when the trailer has no way of determiningwhether the tractor has in fact been decoupled or if the tractor hasmerely been shut off.

The embodiments of the invention surmount this problem by adding theadditional circuit in the trailer-mounted device. A nominal 12-voltsupply 1 from the trailer TL1 is temporarily connected to the Auxiliaryand ABS line 9 through the current limiting resistor 2. This resistor 2is sized to allow a small voltage drop when driving just trailer-mountedloads, but a larger voltage drop when attempting to drive the tractorloads on the switched circuit of the tractor's ignition switch 7. Duringinstallation, the voltage drop due to the trailer alone is measured andrecorded. Thus, if there is a tractor connected, the voltage at theAuxiliary and ABS line 9 will fall to a level below that obtained duringcalibration; if a tractor is not connected, the voltage will be at thecalibration level. Because of the limited current available, none of thetractor loads are energized, and the action of the tractor's ignitionswitch is not compromised. The embodiments of the invention limit thebandwidth and transmission time used.

The embodiments of the invention prevent a remote monitoring systemusing telematics from transmitting false disconnect/reconnect sequencesand confusing a fleet operator.

While embodiments of the invention have been described, it will beevident that the invention may be embodied otherwise.

What is claimed is:
 1. A system comprising: a tractor having an ignitionswitch and an electrical load, a trailer having an electrical load, anelectrical line between the tractor and the trailer and connecting theelectrical load on the trailer with the electrical load in the tractorwhen the tractor is coupled to the trailer, a power source in thetractor to power the electrical load in the tractor through the ignitionswitch and connected to the line for powering electrical load in thetrailer when the trailer is coupled to the tractor, a power arrangementin the trailer and having a given impedance, a test circuit including atest switch between the impedance and said line, said switch when onconnecting said power source to said line, said test circuit, when thetest switch is on, being responsive to when the power arrangement powersonly the electrical load in the trailer and when the power arrangementpowers both the electrical load in the trailer and the electrical loadin the tractor.
 2. A system as in claim 1, wherein said test circuit,when the test switch is on, is responsive to when the power arrangementpowers only the electrical load in the trailer and when the powerarrangement powers both the electrical load in the trailer and theelectrical load in the tractor, when the ignition switch is off.
 3. Asystem as in claim 1, wherein said test circuit includes a transmitter,a wireless link responsive to said transmitter for receiving data fromsaid transmitter, and a management system responsive to said wirelesslink and for sending commands.
 4. A system as in claim 3, wherein saidmanagement system includes means coupled to said test switch to turnsaid test switch on and off.
 5. A system as in claim 1, wherein saidtest circuit includes a metering arrangement responsive to electricalreadings in said electrical loads.
 6. A system as in claim 1, whereinsaid test circuit includes a meter across said loads and in saidtrailer, said transmitter being responsive to said meter.
 7. A fleet ofvehicles, comprising: a plurality of tractors each having an ignitionswitch and an electrical load, a plurality of trailers each having anelectrical load, a plurality of electrical lines each for connectionbetween one of said tractors and one of the trailers and connecting theelectrical load on the one of the trailers with the electrical load inthe one of the tractors when the one of the tractors is coupled to theone of the trailers, a power source in each of the tractors to power theelectrical load in the tractor through the ignition switch and connectedto the one of the electrical lines for powering the electrical load inthe one of the trailers when the one of the trailers is coupled to theone of the tractors, a power arrangement in each of the trailers andhaving a given impedance and connected to the one of said lines, a testcircuit in each of the trailers including a test switch between theimpedance and said one of said lines, said switch when on connectingsaid power source to said one of said lines, said test circuit, when thetest switch is on, being responsive to when the power arrangement powersonly the electrical load in the trailer and when the power arrangementpowers both the electrical load in the trailer and the electrical loadin the tractor, each of said test circuits including a transmitter, awireless link responsive to each of said transmitters for receiving datafrom said transmitter, a management system responsive to said wirelesslink and for sending commands.
 8. A system as in claim 7, wherein ineach of said test circuits, when the test switch is on, is responsive towhen the power arrangement powers only the electrical load in the one ofsaid trailers and when the power arrangement powers both the electricalload in the one of the trailers and the electrical load in the one ofthe tractors, when the ignition switch on the one of said tractors isoff.
 9. A system as in claim 7, wherein said management system includesmeans coupled to said test switches to tum selected ones of said testswitches on and off.
 10. A system as in claim 7, wherein each of saidtest circuits includes a metering arrangement responsive to electricalreadings in said electrical loads.
 11. A system as in claim 7, whereineach of said test circuits includes a meter across said loads and insaid trailers, said transmitter being responsive to said meter.
 12. In atractor-trailer arrangement having an electrical line connecting anelectrical load in the tractor with an electrical load in the trailerthrough a trailer hookup, a method, comprising: connecting a powersource in the trailer through an impedance to said electrical line inthe trailer while the trailer is coupled to the tractor and while thetrailer is uncoupled from the tractor; storing a prevailing electricalcondition at the electrical line while the trailer is one of coupled anddecoupled, as a default condition; intermittently connecting the powersource in the trailer through the impedance to said electrical line inthe trailer and measuring the prevailing electrical condition at theelectrical line; comparing an intermittently measured prevailingcondition with the stored default condition as an indication that thetrailer is coupled to or uncoupled from the tractor.
 13. A method as inclaim 12, wherein said indication is transmitted to a managementarrangement.